Physical vapor deposition (PVD or sputtering) is a well-known process for depositing thin solid films on substrates, and is widely practiced in the semiconductor industry. Ionized physical vapor deposition (IPVD), also referred to as ionized metal plasma (IMP) deposition, has been used more recently to deposit metal films (notably copper) in etched structures such as vias and contact holes. IMP deposition apparatus differs from earlier versions of PVD apparatus in that it requires a metal RF coil in the process chamber in order to generate a plasma which can ionize the metal atoms during the sputter deposition process. The RF coil is, in general, constructed of the same material (with respect to composition and purity) as the sputter target; this is necessary to avoid contamination of the substrate, because sputtering will take place at the coil surface just as at the target surface.
The RF coil is subject to considerable heating due to ion bombardment and high coupled power into the process plasma. The coil temperature may reach 700.degree. C. This in turn causes the temperature of the substrate (typically a semiconductor wafer) to increase; this is not desirable because the substrate temperature cannot be easily controlled. Furthermore, the RF coil is prone to mechanical deformation and premature failure due to the high thermal load. This problem is particularly acute when the coil is constructed of a relatively soft, malleable material such as copper. As shown schematically in FIG. 1, the coil 100 is generally circular in shape with a break in its circumference; the RF voltage is applied across the break through leads 101, 102. Thermal expansion of the coil can cause the ends 111, 112 of the coil to touch, resulting in an electrical short.
There is a need for an RF coil for use in IPVD process apparatus in which excessive heating and deformation are avoided, thereby extending the lifetime of the coil, improving the efficiency and reliability of the IPVD apparatus, and reducing the cost of operating the apparatus in the manufacture of semiconductor devices.